Get them a few free sessions of therapy (disguised as parental consulting or something like that). Overprotective parents will not listen to anyone but their inner overprotective voices. They may listen to a professional, as long as they don't feel contradicted or criticized.
Overprotective parents would rather lose one arm or leg, or both than allow their children to do their will, especially if they are old enough to drive, drink, vote or go to war. That's, according to their logic, when they need more parenting.
I think we misjudged overprotective parents when we label them control freaks. They must be the most experienced people on earth when it comes to anticipating disasters (and they should get some credit for that). While other people are busy making a sack out of their lives, getting themselves into and tying it up (a Venezuelan expression), overprotective parents have been devoting every second on their times working out permutation of all the possible and impossible things that can go wrong during, say, a sleepover, and all the ways to shield their kids from such catastrophes.
For overprotective parents, “free will” is something you get after they are dead, most likely a certified copy of their will, containing all their life-long recommendations along with a power of attorney authorizing the closest old relative who would be able to carry on their overprotective job.
All stories of ghost or apparitions are most likely related to overprotective parents trying to continue their work from the afterlife. Their children have most likely moved to another state or country and that why ghost usually haunt and mess up with perfect strangers. Unable to locate their own, they have to try to protect someone else.
But again, all this can be avoided with good therapy. Let’s just hope the therapists are not themselves overprotective.